[sci.electronics] dimming fluorescent lamps

bender@oobleck.Eng.Sun.COM (I want to be eating rich soup in another town) (02/21/91)

In article <2688@beguine.UUCP> uchuck@uncmed.med.unc.edu () writes:
->We have a problem that maybe some of you may have run across and have
->solved before.  We have a lecture hall that has some 24 fixtures of the 4
->x 48 inch, 40 watt fluorescent lamps.  These require dimming to varying
->degrees depending on the format and subject matter being taught.
->Heretofore we have been using a special dimming ballast which will service
->4 of the fixtures at a time. [...]

on a side note, just how does a dimming ballast work?

mike
--
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whit@milton.u.washington.edu (John Whitmore) (02/21/91)

In article <2688@beguine.UUCP> uchuck@uncmed.med.unc.edu () writes:
>We have a problem that maybe some of you may have run across and have
>solved before.  We have a lecture hall that has some 24 fixtures of the 4
>x 48 inch, 40 watt fluorescent lamps.  These require dimming to varying
>degrees depending on the format and subject matter being taught.
>Heretofore we have been using a special dimming ballast which will service
>4 of the fixtures at a time.  We are down to zero spares and the
>manufacturer does not sell these anymore ...

	You should ask an architect or mechanical engineer (after all,
that's who'd normally specify such an item for new construction) to
check for suppliers of dimmers for fluorescent lamps.

	Failing that, you could install standard fluorescent lamps on
four circuits; switch one turns on four tubes, switch two turns on
eight, switch three turns on sixteen, and switch four turns on
thirty-two.  It's primitive, but it'd give you some control.

	I may be mistaken, but I thought fluorescent lamp dimmers
were relatively simple items, just had a different turn-on phase for
the SCR; such an item wouldn't work right on incandescent bulbs
(and an incandescent dimmer would burn up if connected to a 
fluorescent fixture).  Although a home fix-it store wouldn't
carry such specialized items, probably a builder's hardware store would.

	John Whitmore

ken@hertz.njit.edu (ken ng cccc) (05/08/91)

I hope this thread won't stir up too much controversy.  I currently have
2 sets of 2 20 watt fluorescent lights that I bounce off the ceiling in
order to light the room they are in.  I would like to be able to dim
these lamps for when I don't need them on full strength and to prevent
the temporary blindness when turning them on at 3 am.  Can this be done
with fluorescent lamps?  If I build something with SCR controllers, are
there any noise precautions I should take?  (I presume a ferrite coil
across the power lines and a 0.01 microfarad cap across the SCR itself
will be enough.)

What I have been toying around with is a set of relays (one for each
lamp) to turn the lights on and off in a sequential manner, but I'd
like a better method if possible.

Kenneth Ng
"No problem, this is how you make it" -- R. Barclay, ST: TNG